Rebounding whale populations are good for ocean ecosystems

Far from depleting the resources of ocean ecosystems, growing numbers of large whales may be critical to keeping these environments healthy. That’s the conclusion of a new study, which finds that rebounding populations of baleen and sperm whales may be boosting marine food webs around the world. The work is the latest volley in a long-running debate about the ecological role of whales and how their return to the oceans may affect global fisheries that face myriad threats.

But the new study notes that krill populations remained constant or even declined after great whales experienced big declines. How so? The authors reason that the whales helped provide nutrients critical to krill and other species low on the food web. For instance, the mammals release massive "fecal plumes" and urine streams that fertilize surface waters with nitrogen and iron, the authors note, and help enhance productivity by mixing up the top layers of the ocean when diving.

Another underappreciated contribution to marine ecosystems, the authors report online today in Frontiers in Ecology and the Environment, is the bounty of organic material the animals provide to deep-sea ecosystems when they die. A so-called whale fall of a 40-ton gray whale provides a boost of carbon to the seafloor community equivalent to more than 2000 years of normal detritus and nutrient cycling.

“The reduction of whale carcasses during the age of commercial whaling may have caused some of the earliest human-caused extinctions in the ocean,” writes the study’s first author, conservation biologist Joe Roman of the University of Vermont in Burlington, in an e-mail. “More than 60 species have been discovered that are found only on whale falls in recent decades. By removing this habitat through hunting, we may well have lost many species before we even knew they existed.”

Such new understandings, Roman and his colleagues write, “warrants a shift in view from whales being positively valued as exploitable goods … to one that recognizes that these animals play key roles in healthy marine ecosystems.”

The new study is a useful addition to the debate on the role of whales in global ecosystems, writes marine ecologist Lisa Ballance of the National Oceanic and Atmospheric Administration in San Diego, California, in an e-mail. “As [whales] recover, we can indeed expect their influence on marine ecosystems to change the structure and function of those systems relative to the past 100 years.”